In the processing of metals and in the cleaning of oily and greasy surfaces in the industrial sector, oil-in-water emulsions are frequently formed which must be broken and the oil removed before they are conducted into sewage plants or drainage ditches. The emulsions may be formed by the emulsifiers contained in lubricants, or the oils and fats emulsified by the surfactants contained in the cleaning solution. In cleaning solutions, the emulsions are also broken in order to regenerate them and to prolong their service life.
For degreasing and cleaning of metallic surfaces, particularly in the industrial sector, aqueous solutions which contain tensides and alkali metal hydroxides, as well as builder substances, such as alkali metal carbonates, alkali metal silicates, alkali metal phosphates, alkali metal borates, and also sequestrants, such as phosphonic acids, polyhydroxycarboxylic acids, amino-and polyaminopolycarboxylic acids and organic and/or inorganic corrosion preventives or any combination may be used.
The solution may be neutral to strongly alkaline. As surfacants, the cleaning solutions contain anionic or nonionic tensides and sometimes both. These cleaning solutions are contaminated by petroleum oil or fixed oils and sometimes both and in which emulsifiers, corrosion preventives and other oil additives have been added. These contaminants which are emulsified by possibly emulsifiers contained in oil, and the tensides in the cleaning solution impair the effectiveness of the aqueous cleaning solution until finally it becomes ineffective. The solutions must then be replaced. Before these solutions are discharged they must be freed of oil in accordance with effluent waste disposal requirements. This generally requires breaking the oil-in-water emulsion. It is known that oil-in-water emulsions can be broken by reducing their pH-value to about 1; by salting out the solution; or by adding flocculants, like aluminim or iron salts in a solution in the acid range and neutralizing them again, thereby regenerating them. In order to reduce the emulsification of oil in degreasing solutions, it has also been suggested to use only non-ionic tensides with a turbidity point below 40 deg. C., or to heat the degreasing bath to a temperature above the turbidity point of the tensides in order to obtain oil separation. This method has the disadvantage that it requires a higher temperature of the solution. Besides, the method cannot be used effectively in practice in electrolyte-free solutions.